1. Field of the Invention
The present invention generally relates to devices holding specimens and, more particularly, is concerned with a self-centering vise for holding a specimen in a laboratory instrument, such as a scanning electron microscope.
2. Description of the Prior Art
It is conventional practice to use mechanisms of various designs for holding samples or specimens while they are being examined and analyzed by laboratory instruments. For instance, a holding mechanism must be used to support a sample or part while it is being examined inside the chamber of a scanning electron microscope since the part is completely enclosed within the chamber during the examination.
To allow ease of operation while still maintaining the ability to secure parts of various sizes and shapes, the holding mechanism should have a number of important features. First, the holding mechanism should be self-centering which allows quick installation when loading the instrument and provides the ability to establish the orientation of the part once the instrument is turned on. When the instrument is functioning, the part being analyzed cannot be seen. A cathode ray tube can be seen but is magnified which allows only a small portion of the part to be analyzed at any one time. This can cause disorientation because the entire part is not in view. The self-centering feature will allow returning to a zero X-Y location to regain orientation.
Second, the holding mechanism should have a compact configuration and low profile which allows a part to be examined without the part bumping the top of the instrument. The limited space inside the electron microscope chamber requires efficient use of available altitude when dealing with tall parts. Third the holding mechanism should be lightweight to minimize the load it places on the instrument drive motor so as to allow rotation within the instrument chamber so that different views can be explored.
Fourth, the holding mechanism should utilize materials which avoid contamination that would degrade the high vacuum inside the chamber of the scanning electron microscope. Contaminants such as silicone and petroleum products must not be introduced because chemical analysis data would be altered. Any lubricant used must not volatilize in the high vacuum chamber which would leave a contaminating film in the instrument.
Fifth, because a sample must be electrically conductive and electrically grounded to allow viewing in an electron microscope, the holding mechanism must be a very good electrical conductor.
Sixth, since induced or residual magnetism can deflect the electron beam and cause distortion of the image, the holding mechanism must avoid the use of ferromagnetic materials.
Sample holding mechanisms currently being used fail to incorporate many of the above-outlined features. Consequently, a need exists for a sample holding mechanism incorporating these features to make it particularly suitable for use inside a sealed chamber of a laboratory instrument such as a scanning electron microscope.